U.S. patent number 6,522,952 [Application Number 09/774,173] was granted by the patent office on 2003-02-18 for method and system for controlling cooperative object-transporting robot.
This patent grant is currently assigned to Japan as represented by Secretary of Agency of Industrial Science and Technology. Invention is credited to Hirohiko Arai, Yasuo Hayashibara, Yukinobu Sonoda, Tomohito Takubo, Kazuo Tanie.
United States Patent |
6,522,952 |
Arai , et al. |
February 18, 2003 |
Method and system for controlling cooperative object-transporting
robot
Abstract
A control of a cooperative object-transporting robot which
transports an object in cooperation with a man. The robot shares
substantially a half of the weight of the object with the man,
while the object is kept in a horizontal posture. A force applied
to the robot by the object is detected by a force sensor, and based
on the signal from the force sensor, a motion instruction is output
for the motion components by the rotational force component
.tau..sub.1 around the horizontal axis and the translational force
component Fx.sub.1 in the horizontal back-and-forth direction, upon
setting a gain to reduce the resistance forces of the robot to
small values. The translational force component F.sub.y in the
direction of the object short axis is constrained so that no
translational motion in the direction of the object short axis
occurs.
Inventors: |
Arai; Hirohiko (Tsukuba,
JP), Tanie; Kazuo (Tsukuba, JP),
Hayashibara; Yasuo (Yokohama, JP), Sonoda;
Yukinobu (Kawashi, JP), Takubo; Tomohito
(Tsukuba, JP) |
Assignee: |
Japan as represented by Secretary
of Agency of Industrial Science and Technology (Tokyo,
JP)
|
Family
ID: |
26481876 |
Appl.
No.: |
09/774,173 |
Filed: |
April 19, 2001 |
PCT
Filed: |
March 31, 2000 |
PCT No.: |
PCT/JP00/02079 |
Foreign Application Priority Data
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|
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|
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Jun 1, 1999 [JP] |
|
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11-153158 |
Jun 1, 1999 [JP] |
|
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11-153263 |
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Current U.S.
Class: |
700/258; 414/591;
414/719; 700/245; 700/260; 700/261; 901/16; 901/9 |
Current CPC
Class: |
B25J
9/1679 (20130101); B25J 13/085 (20130101); G05B
2219/36429 (20130101) |
Current International
Class: |
B25J
13/08 (20060101); B25J 9/16 (20060101); G05B
015/00 () |
Field of
Search: |
;700/245,260,261,258,213
;901/2,9,14,16,34 ;414/719,591 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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63-200983 |
|
Aug 1988 |
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JP |
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6-9589 (62-79058) |
|
Feb 1994 |
|
JP |
|
7-205072 |
|
Aug 1995 |
|
JP |
|
2000-176872 |
|
Jun 2000 |
|
JP |
|
Other References
English translation of Japanese article "Control of Man-machine
System Based on Virtual Tool Dynamics" Apr., 1994, Kazuhir Kosuge
et al.* .
English translation of Japanese article "Motion Generation of
Robots in Cooperation with Humans" Sep., 1998, Kazuhiro Kosuge et
al.* .
English translation of Japanese article "Experimental Evalution for
a Robot Carrying an Object with a Human" Jun., 1998, Ikeura et al.*
.
Y. Hayashibara, et al., Proceeding of the 16.sup.th Annual
Conference of the Robotics Society of Japan, vol. 1, pp. 107-108,
"Study on Human Cooperative Behavior Under Carrying Long Objects,"
Sep. 18-20, 1998. .
H. Kozawa, et al., The Japan of Mechanical Engineers, No. 983-1,
pp. 305-306, "Variable Damping Control for a Robot Cooperating with
Human and its Experimental Evalution," Mar. 6, 1998..
|
Primary Examiner: Tran; Khoi H.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed is:
1. A method for control a cooperative object-transporting robot, in
which a man and a robot transport a long object or a large-sized
object in a horizontal plane while grasping each of the ends of the
object, wherein: a force applied to the robot by the object is
detected by a force sensor, and based on the rotational force
component around the vertical axis, and the translational force
component in the direction of the object long axis obtained by
connecting the point grasped by the man and the point grasped by
the robot, each of which is separated from the sensor signal, said
rotational motion component around the vertical axis and said
translational motion component in the direction of the object long
axis are output, upon setting a gain so as to reduce the resistance
forces of the object to small values, while the translational force
component in the direction of the object short axis orthogonal to
said object long axis is constrained so that no translational
motion in the direction of the object short axis occurs, whereby a
motion limitation equivalent to the object being supported by a
virtual wheel facing the direction of the object long axis, at one
point on the robot side, is imposed on the object, and then the
robot arm is driven.
2. A method as claimed in claim 1, wherein: an angle of the
hand-tip of the robot is detected by angle sensors, and based on
the sensor signals, a motion instruction for a translational motion
of the hand-tip in the vertical direction is output so as to keep
the posture of the object horizontal.
3. A system for control a cooperative object-transporting robot, in
which a man and a robot transport a long object or a large-sized
object in a horizontal plane while grasping each of the ends of the
object, said system comprising: a force sensor for detecting a
force applied to the robot by the object; a coordinate converting
part for separating, from the sensor signal, the rotational force
component around the vertical axis, the translating force component
in the direction of the object long axis obtained by connecting the
point grasped by the man and the point grasped by the robot, and
the translating force component in direction of the object short
axis orthogonal thereto; a force-motion converting part which,
based on said rotational force component around the vertical axis
and said translational force component in the direction of the
object long axis, outputs these motion components, using a gain
such as to reduce the resistance forces of the robot in these
rotational direction and translation direction; and a coordinate
converting part for synthesizing these motion components and said
translational force component in the direction of the object short
axis which is set to be zero, and outputting a motion instruction
to drive the robot arm.
Description
TECHNICAL FIELD
The present invention relates to a method and system for
controlling a cooperative object-transporting robot usable in heavy
article transport operations in the mining and manufacturing
industries, the agriculture, forestry, and fishery industries, the
construction industry, the distribution industry, homes, etc.
BACKGROUND ART
One of object-transporting methods in which a man and a robot
cooperatively transport an object, is a method called "power
assist" which has been studied by the California University, the
Tohoku University, the Mechanical Engineering Laboratory of the
Agency of Industrial Science and Technology, etc. This is a
technique in which there are provided two force sensors for
detecting the load of an object grasped by the tip of a robot arm
and a force applied by an operator, respectively, and in which the
robot reduces the load of the operator while moving so as to copy
after the motion of the operator, by amplifying the force applied
by the operator and then applying the amplified force to the
object.
However, in accordance with this method, it is necessary for the
operator to grasp a force sensor handle disposed at the tip of the
robot arm and to move it, and hence the place where a force can be
applied is limited to only one portion of the object. When
transporting a long object or a large-sized object, as shown in
FIG. 1, it is desirable that a hand 2 attached at the tip of the
robot arm 1 and a human operator 3 grasp, for example, each of the
ends of the object 4 and support the object 4. However, in this
case, while a force can be measured on the robot arm 1 side by
providing a force sensor 5, a force applied to the object 4 cannot
be directly measured on the operator 3 side. This makes it
difficult to apply the above-described "power assist"
technique.
On the other hand, the Stanford University in U.S., the Tohoku
University, etc. has studied a method in which a man and a robot
support an object at some portions thereof and in which they
transport the object while sharing the load therebetween. This
method is primarily based on impedance control. Specifically, in
this method, an object is supported under weightless conditions by
compensating for the weight of the object, and simultaneously
virtual impedances (inertia, viscosity, and spring coefficient) are
set with respect to the object or the robot, whereby the motion of
the object is changed in response to the change in the force
applied by the man, and the motion of the object is caused to copy
after the motion of the man.
In order to compensate for the gravity acting on the object,
however, it is necessary to know in advance the mass or the mass
distribution of the object. This hinders this method from being
flexibly applied to the transportation of various objects.
When the object is a long object, it is virtually only a
translational force which a man can apply. It is difficult to apply
a torque (rotational force) to one end of an object to be
transported. In the case of a control based on impedance control, a
straight-ahead motion in the direction of the long axis obtained by
connecting the man and the robot is easy, but with regard to a
motion including rotation, it is difficult for man to positionally
control the end point of the robot side as a target point. In order
to move the body by applying a small force, it is necessary to set
impedance parameters such as inertia and viscosity to be low
values. In this case, however, a drift (slipping motion) in the
normal direction is generated, and the drift is difficult to stop.
This raises a problem that it is difficult to intuitively forecast
behavior of the object.
The reason that the above-described problems associated with the
conventional art is caused is because the impedance parameters are
set to be uniform in all directions, and also they are set to be in
an absolute coordinate space. As a result, behavior of the object
becomes one which man has never daily experienced, so to speak, a
case like as if the object floating in a weightless space were
moved by a force applied. This makes operations of making the
object reach a target position and posture difficult.
DISCLOSURE OF INVENTION
It is an object of the present invention to solve the
above-described problems, and to achieve a controlling means for
making the arm of a cooperative object-transporting robot share
approximately a half of the weight of an long object, in the robot
control in which a man and the robot grasp each of the ends of the
long object, sharing the load due to the weight thereof.
It is another object of the present invention to achieve a
controlling means for a cooperative object-transporting robot, the
controlling means having only to have one sensor for measuring a
force applied to the robot arm by an object, as a force sensor,
without the need to have a sensor for measuring a force by an
operator, and the controlling means not being required to know the
dimensions and the mass of the object in advance.
It is still another object of the present invention to permit a man
to intuitively perceive the behavior of the object by the daily
senses thereof in the control for the above-described cooperative
object-transporting robot, by simplifying the relationship between
the force applied by the man and the motion of the object by
limiting the direction in which the object is movable.
It is a further object of the present invention to achieve a
controlling means for a cooperative object-transporting robot, the
controlling means permitting a man to intuitively perceive the
above-described behavior of the object by the daily senses, without
deviating from the original operational purpose of making the
object reach arbitrary target position and posture.
In order to achieve the above-described purposes, the controlling
method in accordance with the present invention, which is
essentially a controlling method for controlling the cooperative
object-transporting robot in order that a man and the robot
transport a long object or a large-sized object while grasping each
of the ends thereof, is characterized in that an angle of the
hand-tip of the robot is detected by angle sensors, and that, based
on the sensor signals, a motion instruction for a translational
motion of the hand-tip in the vertical direction is output so as to
keep the posture of the object horizontal.
The above-described controlling method may be such that a force
applied to the robot by the object and an angle of the hand-tip of
the robot are detected by sensors, and that, based on the sensor
signals, a motion instruction to drive the robot arm is output for
the rotational motion component around the horizontal axis and the
translational motion component in the horizontal back-and-forth
direction, upon setting a gain so as to reduce the resistance
forces of the robot to small values.
On the other hand, the controlling system in accordance with the
present invention is essentially a controlling system for
controlling the cooperative object-transporting robot in order that
a man and the robot transport a long object or a large-sized object
while grasping each of the ends thereof, and is characterized by
angle sensors for detecting an object-grasping angle of the
hand-tip of the robot, a motion converting part for outputting the
motion component of the hand-tip in the vertical direction so as to
keep the posture of the object horizontal, based on the hand-tip
angle detected by the angle sensors, and a coordinate converting
part for outputting a motion instruction to drive the robot arm,
based on the above-mentioned motion component.
The above-described controlling system may comprise a force sensor
for detecting a force applied to the robot by the object, a
coordinate converting part for separating the rotational force
component around the horizontal axis and the translational force
component in the horizontal back-and-forth direction, from the
sensor signal of the force sensor, a force-motion converting part
for outputting these motion components, using a gain such as to
reduce the resistance forces of the robot in these rotational
direction and translation direction to small values, based on the
above-mentioned two force components, and a coordinate converting
part for synthesizing these motion components and outputting a
motion instruction to drive the robot arm.
In accordance with the controlling means for the cooperative
object-transporting robot having the above-described constitution,
when controlling the cooperative object-transporting robot which is
arranged so that a man and the robot grasp each of the ends of the
object, and that they transport the object sharing the load due to
the weight thereof, it is possible to control so that the robot arm
shares approximately a half of the weight of the object, by
controlling the translational motion of the hand-tip in the
vertical direction so as to keep the posture of the object
horizontal. Simultaneously, it is possible to control the
rotational motion of the hand-tip of the robot so that the
rotational force at the hand-tip thereof becomes zero. As a force
sensor, it is essential only that one sensor for measuring a force
applied to the robot arm by an object is provided. There is no need
for sensor for measuring a force by an operator. Also, it is
unnecessary to know in advance the dimensions and the mass of the
object.
Next, a second controlling method is a controlling method for
controlling the cooperative object-transporting robot in order that
a man and the robot transport a long object or a large-sized object
in a horizontal plane while grasping each of the ends thereof, and
is characterized in that a force applied to the robot by the object
is detected by a force sensor, and that, based on the rotational
force component around the vertical axis, and the translational
force component in the direction of the object long axis obtained
by connecting the point grasped by the man and the point grasped by
the robot, each of which is separated from the sensor signal, the
above-mentioned rotational motion component around the vertical
axis and the above-mentioned translational motion component in
direction of the object long axis are output, upon setting a gain
so as to reduce the resistance forces of the object to small
values, while the translational force component in the direction of
the object short axis orthogonal to above-mentioned object long
axis is constrained so that no translational motion in the
direction of the object short axis occurs, whereby a motion
limitation equivalent to the object being supported by a virtual
wheel facing the direction of the object long axis, at one point on
the robot side, is imposed on the object, and then the robot arm is
driven. Furthermore, in such a controlling method, the control may
also be performed on the precondition that an angle of the hand-tip
of the robot is detected by angle sensors, and that, based on the
sensor signals, a motion instruction for a translational motion of
the hand-tip in the vertical direction is output so as to keep the
posture of the object horizontal.
Moreover, a second controlling system is a controlling system for
controlling the cooperative object-transporting robot in order that
a man and the robot transport a long object or a large-sized object
in a horizontal plane while grasping each of the ends thereof, and
is characterized by a force sensor for detecting a force applied to
the robot by the object, a coordinate converting part for
separating, from the sensor signal, the rotational force component
around the vertical axis, the translating force component in the
direction of the object long axis obtained by connecting the point
grasped by the man and the point grasped by the robot, and the
translating force component in direction of the object short axis
orthogonal thereto, a force-motion converting part which, based on
the above-mentioned rotational force component around the vertical
axis and the above-mentioned translational force component in the
direction of the object long axis, outputs these motion components,
using a gain such as to reduce the resistance forces of the robot
in these rotational direction and translation direction, and a
coordinate converting part for synthesizing these motion components
and the above-mentioned translational force component in the
direction of the object short axis which is set to be zero, and
outputting a motion instruction to drive the robot arm.
In accordance with the controlling means for the cooperative
object-transporting robot having the above-described constitution,
when controlling the cooperative object-transporting robot which is
arranged so that a man and the robot transport a long object or a
large-sized object in the horizontal plane while grasping each of
the ends thereof, a motion limitation equivalent to the object
being supported by a virtual wheel facing the direction of the
object long axis, at one point on the robot side, is imposed on the
object, and thereby the direction in which the object is movable is
limited. This simplifies the relationship between the force applied
by the operator and the motion of the object, and permits the
operator to intuitively perceive the behavior of the object by
daily senses thereof. In addition, there is no fear of deviating
from the original operational purpose of making the object reach
arbitrary target position and posture.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is an explanatory view for a cooperative object-transporting
robot controlled based on the present invention.
FIG. 2 is an explanatory view for the detected output component of
the force sensor used in a first control of the cooperative
object-transporting robot in accordance with the present
invention.
FIG. 3 is a construction view showing the first control system of
the cooperative object-transporting robot in the present
invention.
FIG. 4 is a conceptual explanatory view for a second control in
accordance with the present invention.
FIG. 5 is an explanatory view for the detected output component of
the force sensor used in the second control of the cooperative
object-transporting robot in accordance with the present
invention.
FIG. 6 is a construction view showing the second control system of
the cooperative object-transporting robot in the present
invention.
BEST MODE FOR CARRYING OUT THE INVENTION
When a man and the robot cooperatively transport an object while
grasping each of the ends of the object, the most important thing
is how the weight of the object is to be shared therebetween. In
general, if the object is supported only by a translational force
without applying a torque (rotational force) at the point where the
object is supported, a vertical force will be distributed in an
inverse proportion to the distance from the barycenter of the
object. In many cases, a long object has a substantially uniform
mass distribution, and hence, if no torque is applied to the object
by the tip of the robot and the tip of the object is freely
rotatable, the man and the robot will share the weight
substantially half-and-half, irrespective of the mass and
dimensions of the long object.
Meanwhile, in the transportation of a long object, the object will
be transferred while keeping the posture thereof horizontal in the
majority of cases. It is therefore preferable that the vertical
motion of the robot tip be controlled so that the tilt of the
object is canceled out. Specifically, when the object tilts by
being lifted by the man, the tilt of the object will be canceled
out and the object will be able to keep the posture thereof
horizontal if the robot is caused to lift the object, as well. The
same goes for the case where the object is lowered.
With regard to a horizontal motion of the object, it is preferable
that the robot move so as to copy after the force applied to the
body by the man. That is, if virtual inertia and viscosity are set
with respect to the horizontal motion of the robot tip, and
sufficiently low values thereof are selected, it will be possible
to realize a motion copying after that of the man without providing
a resistance force to the man.
Specifically, as shown in FIGS. 1 and 2, a force sensor 5 is
provided between a robot arm 1 and a hand 2 disposed at the tip
thereof, and by this force sensor 5, a force applied to the robot
arm 1 side by the operator side Q via an object 4 is detected at an
object-supporting point P on the robot side of the object 4. Then,
the signal obtained is analyzed into the translational force
component Fx.sub.1 in the horizontal back-and-forth direction (PQ
direction), the translational force component Fz in the vertical
direction (PR direction), and the rotational force component
.tau..sub.1 around the horizontal axis around the point P.
Although not shown in the figures, each of the joints of the robot
arm has a joint actuator for driving each of the joints, and has an
angle sensor for detecting the joint angle. A tilt angle .theta. of
the object is detected based on sensor signals of these angle
sensors.
With regard to the translational force component Fx.sub.1 in the
horizontal back-and-forth direction and the rotational force
components .tau..sub.1, the horizontal velocity at the point 4 on
the object and the rotational velocity at the hand-tip are
determined so that the robot moves without resistance with respect
to respective direction. Also, the vertical velocity at the point P
for making the posture of object 4 horizontal in proportion to the
tilt angle .theta. of the object 4, is determined.
For these purposes, based on the rotational force component
.tau..sub.1 around the horizontal axis and the translational force
component Fx.sub.1 in the horizontal back-and-forth direction in a
sensor signal of the force sensor 5, the robot arm is driven by
outputting the rotational motion component around the horizontal
axis and the translational motion component in the horizontal
back-and-forth direction, upon setting a gain so as to reduce the
resistance forces of the robot to small values. On the other hand,
with regard to the hand-tip angle (tilt angle .theta. of the object
4) detected by the angle sensors at the hand-tip, a motion
instruction is output for a translational motion in the vertical
direction in proportion to the hand-tip angle, and thereby the
hand-tip of the robot arm is driven upward and downward so as to
keep the posture of the object horizontal.
In this way, around the point (point P in FIG. 2) where the robot
supports the object, since the object is freely rotatable and no
torque is applied to the object, the forces by the man and the
robot in the vertical direction become substantially half-and-half
in accordance with the mass distribution of the long object. Also,
when the man applies a horizontal force to the object, the robot
moves horizontally following it without resistance. When the object
tilts by being lifted by the man, a velocity upward in the vertical
direction such as to make the tilt angle zero occurs in the
hand-tip of the robot, and hence the object rises while keeping the
posture thereof horizontal. The same goes for the case where the
object grasped by the mans is lowered.
It can be said that such a control is a control in which an
impedance control is performed with respect to the horizontal
direction while an initial state of the object is maintained with
respect to the vertical direction.
In order to execute the above-described controlling method, a
system described hereinafter with reference to FIGS. 2 and 3 may be
used.
As shown in FIG. 2, the tip of a robot arm 1 need to have a hand 2
for grasping an object 4 and a force sensor 5 for detecting a force
applied by an operator via the object 4. Also, as described above,
each of the joints of the robot arm has an joint actuator for
driving each of the joints, and has an angle sensor for detecting
the joint angle. Meanwhile, as these joint actuators and angle
sensors, those which are generally provided for robot arms which
are subjected to a drive control, are utilized as they are.
The sensor signal detected by the force sensor 5 is input to a
controlling system (computer). In this controlling system, as shown
in FIG. 3, the translational force component Fx.sub.1 in the
horizontal back-and-forth direction, the translational force
component Fz in the vertical direction, and the rotational force
component .tau..sub.1 around the horizontal axis are separated in a
coordinate converting part (a).
On the other hand, in the angle sensor of each of the joints of the
robot arm, a tilt angle .theta. of the object 4 is measured.
In a force-motion converting part, based on the above-described
translational force component Fx.sub.1 in the horizontal
back-and-forth direction, the translational motion component
(velocity and acceleration) in the PQ direction at the point P in
FIG. 2 is determined by the operation such as the following
equation (1). Also, based on the rotational force component
.tau..sub.1 around the horizontal axis, the rotational motion
component (angular velocity and angular acceleration) around the
point P is determined by the operation such as the following
equation (2). These are determined based on the setting of the gain
such as to reduce the resistance forces of the robot in the
rotation direction and the translation direction to small values.
##EQU1##
Here, in order to reduce the resistance forces of the robot to
small values, a target inertia coefficient M, a target inertia
moment coefficient I, a target viscous friction coefficient Bx, and
a target viscous friction coefficient Bd are each set to be low
values.
On the other hand, based on the tilt angle which has been detected
by the angle sensors and which has been determined in a coordinate
converting part (b), the translational motion component (velocity)
in the vertical direction at the point P is determined in a motion
converting part, as being proportional to the tilt angle .theta. of
the object, as shown in equation (3).
A coordinate converting part (c) synthesizes the above-described
motion components, thereby determines the motion of the hand-tip of
the robot arm 1, and outputs a motion instruction to drive each of
the joint actuators. The motion of each of the joint actuators is
detected by the angle sensor provided at each of the joints, and
the position and the driving velocity of each of the joints are fed
back so that the motion of the robot arm approaches the target
values.
Next, the second controlling means in accordance with the present
invention will be described with reference to FIGS. 4 through 6. In
this control, the following method and system may be constituted on
the precondition that the above-described hand-tip angle of the
robot is detected by the angle sensors, and that, based on the
sensor signals, a motion instruction is output for a translational
motion in the vertical direction so as to keep the posture of the
object horizontal.
Man frequently experiences daily an operation in which an object is
placed on a cart having passive wheels, and in which the object is
carried while the cart is pushed on a horizontal floor, when using
a single-wheel carrier (so-called "wheelbarrow"), a shopping cart,
a baby carriage, a table wagon, or the like.
In these cases, the direction in which the cart is movable is
momentarily limited by the direction of the wheels. Specifically,
in the direction in parallel with the wheels, the cart can be moved
to and fro by the rotation of the wheels, but in the direction in
orthogonal to the wheels, the cart cannot be moved unless the
wheels are slipped sideway against the friction between the floor
surface and the wheels. Such a kind of motion limitation is called
a "nonholonomic constraint".
Despite of such a limitation of the motion direction, it is
possible to ultimately make the cart reach arbitrary target
position and posture by pushing the cart along an appropriate
trajectory, and this has been mathematically verified. In reality,
man has generally a skill to practice it based on daily
experiences.
As shown in FIG. 1, even when the hand 2 of the robot arm 1 and the
operator 3 grasp each of the sides of a long object or a
large-sized object 4, and cooperatively transport it face to face
in a horizontal plane, the man can intuitively perceive the
behavior of the object if he/she controls the robot so that the
object 4 conducts the same behavior as that of the cart. This makes
it possible to easily make the object reach a target position and
posture. For this purpose, as illustrated in FIG. 4, a motion
limitation such that the object 4 is supported by a virtual wheel 6
facing the object long axis, on the robot side 4a, is preferably
imposed on the object 4. This permits the operator side 4b to
perform the same operation as the case where the operator side
transports the object while pushing the cart in an appropriate
direction which is exemplified by the arrow.
Specifically, as illustrated in FIG. 5, a force sensor 5 is
provided between a rod arm 1 and a hand 2 disposed at the tip
thereof, and by this force sensor 5, a force applied to the robot
arm 1 side by the operator side Q via an object 4 is detected at
one point P on the robot side of the object 4. Then, the signal
obtained is analyzed into the translational force component
FX.sub.2 in the direction (PQ direction) of the object long axis
obtained by connecting the operator and the robot, the
translational force component Fy in the direction (PR direction)
orthogonal thereto, and the rotational force component .tau..sub.2
around the vertical axis at the point P. With regard to the
rotational force component .tau..sub.2 and the translational force
component Fx.sub.2 in the long axis direction, the robot is
permitted to move without resistance with respect to respective
direction, while, with regard to the translational force component
Fy, the motion of the robot is limited. This results in that an
equivalent motion limitation to the object 4 being supported by a
virtual wheel facing the direction of the object long axis, at the
point P, is imposed on the object.
For these purposes, based on the rotational force component
.tau..sub.2 around the vertical axis and the translational force
component FX.sub.2 in the direction of the object long axis in a
sensor signal of the force sensor 5, the rotational motion
component around the vertical axis and the translational motion
component in direction of the object long axis are output, upon
setting a gain so as to reduce the resistance forces of the robot
to small values. On the other hand, the translational force
component Fy in the direction of the object short axis is
constrained so that no translational motion in the direction of the
object short axis occurs, and then the robot arm is driven. Herein,
this constraint for preventing the translational motion component
in direction of the object short axis from occurring is achieved by
outputting the motion instruction such that the motion component in
the direction of the object short axis becomes substantially
zero.
In this way, the point P on the object 4 shown in FIG. 5 is
permitted to translate only in the PQ direction. In addition, the
point P is permitted to be rotated therearound. Furthermore, the
point P is also permitted to successively vary the travelling
directions thereof while proceeding along a smooth curved
trajectory tangent to the straight line PQ. Since the behavior of
the object 4 is the same as the case where it is supported by the
wheel at the point P, the operator can intuitively make the object
reach a target position and posture, using the same skill as the
case where the operator pushes a cart.
In order to execute the above-described first controlling method, a
second system described hereinafter with reference to FIGS. 5 and 6
may be used.
As shown in FIG. 5, the tip of the robot arm 1 need to have a hand
2 for grasping an object 4 and have a force sensor 5 for detecting
a force applied by an operator via the object 4. The sensor signal
detected by the force sensor 5 is input to a controlling system
(computer). In this controlling system, as shown in FIG. 6, the
translational force component Fx.sub.2 in the direction of the
object long axis, the translational force component Fy in the
direction of the object short axis, and the rotational force
component .tau..sub.2 around the vertical axis are separated in a
coordinate converting part (1).
In a force-motion converting part, the translational motion
component (velocity and acceleration) in the PQ direction at the
point P in FIG. 5 is determined based on the above-described
translational force component Fx.sub.2 in the direction of the
object long axis, and the rotational motion component (angular
velocity and angular acceleration) around the point P is determined
based on the rotational force component .tau..sub.2 around the
vertical horizontal axis. The determination of these motion
components is based on the setting of a gain such as to reduce the
resistance forces of the robot in the rotation direction and the
translation direction to small values. On the other hand, with
regard to the translational force component Fy in the direction of
the short axis, the translational motion component (velocity and
acceleration) in the PR direction, at the point P, is set to be
zero irrespective of the output of the force sensor. These motion
components are synthesized in a force-motion converting part (2),
and a motion instruction to drive each of the joint actuators of
the robot arm 1 is output. The motion of each of the joint
actuators is detected by an angle sensor provided at each of the
joints, and the position and the driving velocity of each of the
joints are fed back so that the motion of the robot arm approaches
the target values.
* * * * *